TYPHOID FEVER 303 



surface of agar. The agar reveals a growth in about twenty-four 

 hours at 37° C, which is the favourable temperature. A greyish, 

 moist, irregular growth appears, but it is invariably attached to 

 the track of the inoculating needle. On agar plates the superficial 

 colonies appear as circular spots, dull white by reflected light and 

 bluish-grey by transmitted light. The deep colonies are opaque 

 and finely granular. On gelatine the growth is much the same, but 

 its irregular edge is, if anything, more apparent. There is no 

 liquefaction and no gas formation. On plates of gelatine the 

 colonies become large and spreading, with wavy margins. The whole 

 colony appears raised and almost limpet-shaped, with delicate lines 

 passing over its surface. When magnified, there is an appearance 

 of transparent iridescence. The growth on potato is termed 

 " invisible," and is of the nature of a potato-coloured pellicle, which 

 appears to be moist, and may at a later stage become light brown 

 in colour, particularly if the potato is fresh. Milk is a favourable 

 medium, and is rendered slightly acid. No coagulation takes place. 

 Broth is rendered turbid, and there is the formation of a sediment. 

 The organism is stained with carbol-thionin blue, carbolic fuchsin, 

 etc. It is decolorised by Gram's methods. 



The problem of isolating the typhoid bacillus is greatly com- 

 plicated by the fact that B. coli communis is a normal inhabitant 

 of the alimentary canal, is widely distributed in nature, and is in 

 many respects similar to the typhoid bacillus. (For full account 

 of B. coli and its similarities to the typhoid bacillus, see pp. 46-51.) 



We have pointed out elsewhere the relation between soil and 

 typhoid. In water, even though we know it is a vehicle of the 

 disease, the Bacillus typhosus- has been only very rarely detected. 

 The difficulties in separating the bacillus from water (hke that at 

 Maidstone, for example), which appears definitely to have been the 

 vehicle of the disease, are manifold. To begin with, the enormous 

 dilution must be borne in mind, a comparatively small amount of 

 contamination being introduced into large quantities of water. 

 Secondly, the group of the B. coli species considerably complicates 

 the search. 



Further, we must bear in mind a point that is frequently neglected, 

 namely, that the bacteriological examination of a water which is 

 suspected of having conveyed the disease is from a variety of circum- 

 stances conducted too late to detect the causal bacteria. The in- 

 cubation period of typhoid we may take at fourteen days. Let us 

 suppose a town water supply is polluted with some typhoid excreta 

 on the 1st of January. Until the 14th of January there may be 

 no knowledge whatever of the state of affairs. Two or three days 

 are required for notification of cases. Several more days elapse 

 generally before bacteriological evidence is demanded. Hence arises 



